This invention relates to a vehicle thermal testing method and apparatus and is an improvement in or modification of the brake testing method and apparatus disclosed in our prior-published specification EP-A-0 729 018 (our reference P52580EP). The present invention is principally applicable to thermal testing of automotive wheel assemblies including brakes and wheels and tires and rim assemblies for identifying thermal imbalance arising particularly from braking imbalance, but which is also applicable to identifying tire temperature imbalance and other factors such as wheel bearing temperature imbalance. Indeed, the present invention provides a method and apparatus which is so quick and convenient to use that it is applicable to any vehicle including railway vehicles and aircraft where testing of nominally thermally balanced locations for (potentially) minor temperature differences may reveal (the beginnings or symptoms of) important differences in settings or conditions or load. The invention is also applicable to the testing of vehicle systems which, in use, are thermally stable but operate at (determinable) different temperatures, and such use of the invention may extend to vehicle engine and transmission systems and of course to braking systems other than friction braking systems, including electrical brakes. A particular application of the invention is to aircraft braking systems and to monitoring the operation of same, particularly in high stress situations such as after a rejected take-off where the thermal load in the system leads to very high temperatures. Equally, the invention is applicable to the detection of brakes or other systems which are not generating sufficient (or any) heat.
The invention provides a means for quickly and conveniently assessing a thermal distribution system for imbalance or other irregularity detection. The system offers a simple means to identify the seat of a potential or developing problem.
The specification of our prior EP application discloses a method and apparatus for analysis of brakes in automotive vehicles. Spot-type infra-red thermometers are employed to sense localised temperature elevation produced by brake application, sensing at spot zones located on, for example, wheel nuts/studs which provide a thermal transfer route from the brake drums or discs. Analysis of the thermal data from the sensors includes a peak detect-and-hold function. Comparison of the thermal data enables detection of braking imbalance.
The brake testing system of our prior EP specification has proved to be of significant practical applicability for the routine testing of automotive braking systems, particularly in view of the relative simplicity of the equipment involved and the scope provided for relatively accurate determination of braking imbalance. Thus, the system does not require the use of roller systems and associated kinetic energy measurement systems. The equipment involved in the system of our prior EP specification is largely based upon off-the-shelf infrared spot sensor devices which are used in combination with software-intensive data processing systems of the kind which can be provided for a dedicated function of this kind at increasingly satisfactory low initial costs as original equipment.
In summary, the system of our prior EP specification offers the prospect for simple roadside testing of vehicle braking operations utilising lightweight mobile equipment leading to immediate meaningful results, and without the complications or expense inherent in prior systems.
Nevertheless, the system disclosed in our prior EP specification is itself susceptible of improvement, notably in relation to the facilities provided for the physical implementation of the test routines, notably the measures provided for ensuring proper and convenient and rapid and effective inputting of thermal data, including alignment of the sensor device with the relevant portion of each wheel to be tested. Also, there is a need for the provision of a system whereby the sequential tests to be carried out on one or more wheels of a vehicle are carried out in the appropriate and proper sequence so that data is properly compared between wheels on the same or opposite sides of the vehicle according to the requirements of the test in question.
Clearly, if possible such a system should be implemented in a very simple and/or practical and/or rapid manner utilising lightweight and/or easily operated and/or cost-effective equipment which somehow minimises the opportunities for the introduction of operational errors by the technical personnel carrying out the tests.
An object of the present invention is to provide a method and apparatus providing improvements in relation to one or more of the matters discussed above, or generally.
According to the invention there is provided a method and apparatus applicable to the thermal analysis of vehicle wheels and other heat generating assemblies including brake and tire performance in automotive and other vehicles, as defined in the accompanying claims.
In an embodiment of the invention described below there is provided a method and apparatus for analysis of brake performance in automotive vehicles in which data is inputted to the sensing means and/or to a test control system associated therewith, relating to vehicle type or wheel or brake characteristics, and a mobile testing handset of said sensor means is caused to generate testing instructions in accordance with the method to be carried out for a given vehicle type or wheel or brake characteristics under test. Moreover, the testing steps carried out in accordance with the instructions displayed by the handset, such steps relating to at least one axle of the vehicle, are carried out in a sequence defined and in accordance with the instructions and this sequence includes a repetition of at least one step of the sequence so that allowance made for the effect of the time taken to carry out the sequence of steps can be checked and adjusted if necessary.
Accordingly, it can be seen that in this way, by the provision of a mobile handset, there is provided a simple means in which the practical and manual implementation of the thermal testing system is greatly facilitated. The use of a manual handset having (if desired or necessary) an appropriate communications link to a base station is in itself a practical step forward which enables the technical operative carrying out the test more easily and rapidly to manipulate the equipment.
In addition, the handset enables easy positioning of the infrared spot sensor in a defined location in relation to a vehicle wheel. For example, a simple location-and-distance-defining locater device can be utilised to define a fixed distance with respect to wheel nuts so that all that the operative needs to do is to place the locater device over a wheel nut of the relevant wheel of the vehicle and the sensing distance and sensing attitude are thereby effectively and accurately defined. One important source of test error is thereby reduced or eliminated. In such a system the infrared spot sensor can be of the fixed focus kind which greatly simplifies its construction and reduces it cost. Alteratively, a non-mechanical locator device such as a laser spot pointer can be used to ensure accurate alignment, and in such a system the infrared spot sensor needs to have adjustable focus functionality to provide validity in the thermal comparison step in the method of the invention.
As to the sequence of steps which needs to be carried out, in accordance with the described embodiment the handset itself is caused to display the necessary instructions for the proper sequence of test operations. For example, the handset may be provided with a display device representing one or more aspects of the construction of the vehicle is wheels or braking system together with the provision of light-emitting-diodes at opposite ends of a simulated axle so that light pulses generated by the LED""s can directly and accurately instruct the user which wheel to carry out the next test at. Also, the arrangement can be such that the LEDs signal the required duration of a given test and likewise indicate when the handset can be removed from the particular wheel nut or other structure on the wheel. In the case when the method is to be used to compare the wheels of (say) two stub axles at opposite sides of the vehicle, then the xe2x80x9cinstructionsxe2x80x9d may amount to no more than an indication of when the first test (on one wheel) is complete and likewise for the second test. It will be understood that in the case of a simple system intended only (or mainly) to check braking balance between two wheels on opposite sides (or the same side) of the vehicle, then the extent of instructions needed for this purpose is correspondingly limited provided the user applies the handset to the wheel nuts for a sufficient period to enable the temperature to be clearly sensed, and provided also that the time interval between the test on one wheel and the next test is reasonably short.
By arranging the test sequence so that at least one step in the sequence is repeated, allowance can readily be made (by Newton""s law of cooling) for the effect of the time taken to carry out the sequence of steps, and this allowance can be checked and adjusted if necessary. The system checks for ambient temperature and allows for this accordingly. Thus, another variable which inevitably would otherwise introduce inconsistency between different operatives carrying out the test, or indeed between successive tests carried out by one operative, is thereby largely reduced or eliminated. In the case where an operative is required to carry out the test at a defined speed (in a fixed time) and/or where the effect of heat losses can be ignored (high ambient temperature or rapidly-executed tests) it may be acceptable not to repeat one of the tests while still obtaining an acceptably accurate result.
Thus, the described embodiment provides a practical and readily utilised system for automotive brake imbalance testing in which the variables arising from matters discussed above are either reduced, eliminated or rendered controllable so as to enable the method and apparatus to produce results which are statistically greatly improved.
In the embodiment described below, the algorithm employed in the thermal comparison function is constructed such that the side-to-side (or same side) imbalance calculations produce results indicating pass or check or fail levels of 0.15% imbalance, 16 to 30% imbalance, and above 30% imbalance respectively. These figures are designed to correlate with the percentage imbalances achieved using brake force measured on standard roller-type brake testers.